Continuously transposed conductors (“CTCs”) or CTC cables include a number of multiple parallel strands that are individually insulated and formed into an assembly. Typically, the strands of a CTC cable are formed into two interposed stacks, and each strand is transposed in turn to each position within the cable. Each strand may successively and repeatedly take on each possible position within a cross-section of the CTC cable. CTC cables are typically used to form windings in electrical devices, such as electrical transformers.
The individual strands of a CTC cable are typically formed by applying one or more insulating enamel coatings onto an elongated conductor. The traditional insulation for each strand is polyvinyl acetate (“PVA”), and the PVA is applied in successive layers as the strand makes multiple passes through an enameling oven. Each pass through the oven facilitates evaporation of solvents and curing of the PVA layer, and multiple passes are required to achieve a desired enamel film thickness and desired enamel properties.
The traditional method of enameling individual strands for a CTC cable is problematic for several reasons. First, the enamel typically only contains between 15% and 23% solids by volume at the time of application. In other words, 76% to 85% of the applied material typically consists of solvent that is present only for the purpose of liquefaction and transportation of the enamel. Conventional solvents are typically highly volatile materials that must be handled with care and disposed of in a manner that satisfies environmental regulations. The formed enamels are also often subject to environmental regulations, which contributes to higher disposal costs. Additionally, during formation of an enamel layer, significant heating energy is required to drive off the solvents from the enamel and to crosslink the enamel to provide desired final properties. Typically, only about 10% to 15% of the applied heat is actually used in the enamel curing process, resulting in a relatively energy inefficient process. The heat and time required to optimize the evaporation rate required to drive off the solvents from the enamel also impairs wire line speed and the resulting throughput of the enameling oven. Accordingly, there is an opportunity for improved CTC cables.